Learn AI Create the Future — with Pranay
Main site

LeetCode solutions

10. Regular Expression Matching

My accepted Python solution to LeetCode problem 10, Regular Expression Matching, running in 8ms.

  • Difficulty: Hard
  • Python
  • Runtime 8ms
  • Memory 17.3MB

Read the problem on LeetCode View on GitHub

The problem statement is LeetCode’s and stays on their site. What follows is my accepted solution.

Python

Accepted on LeetCode — runtime 8ms, memory 17.3MB, accepted 2025-12-29.

python
class Solution:
    def isMatch(self, s: str, p: str) -> bool:
        m, n = len(s), len(p)
        
        # dp[i][j] = True if s[:i] matches p[:j]
        dp = [[False] * (n + 1) for _ in range(m + 1)]
        dp[0][0] = True
        
        # Handle patterns like a*, a*b*, a*b*c*
        for j in range(2, n + 1):
            if p[j - 1] == '*':
                dp[0][j] = dp[0][j - 2]
        
        for i in range(1, m + 1):
            for j in range(1, n + 1):
                if p[j - 1] == '*':
                    # Match zero occurrences
                    dp[i][j] = dp[i][j - 2]
                    # Match one or more occurrences
                    if p[j - 2] == '.' or p[j - 2] == s[i - 1]:
                        dp[i][j] = dp[i][j] or dp[i - 1][j]
                elif p[j - 1] == '.' or p[j - 1] == s[i - 1]:
                    dp[i][j] = dp[i - 1][j - 1]
        
        return dp[m][n]

Source